This invention relates to an apparatus that provides communication between a probe and a sensor. More particularly, but not by way of limitation, this invention relates to an apparatus and method that provides communication between a probe located in the central bore of a drill collar and sensor electronics located in the drill collar wall.
In the course of drilling wells, an operator finds it necessary to learn geologic properties of the subterranean zones. Regardless of whether the zones contain hydrocarbons, the knowledge of specific features and characteristics of the various reservoirs is imperative for the economical exploitation of a field. One way to obtain geologic information of the formation is to lower a probe on a wire line. The probe may contain various sensors such as resistivity, gamma ray, gamma density, neutron porosity, pressure, etc. As those of ordinary skill in the art will recognize, the probes may be lowered in open hole situations intermittent of drilling operations, or in post drilling applications where the well contains casing. These type of operations are commonly referred to as well logging.
Another prior art technique is the use of sensors during actual drilling operations. Two techniques commonly used in the industry are logging while drilling (LWD) and measurement while drilling (MWD) devices. Both the LWD and MWD devices employ sensors that collects specific types of information, and wherein that information is transferred to a down hole processor. The down hole processor in turn transmits the information to the surface. The transmission media may be a cable that electrically connects the down hole processor to a surface processor. Alternatively, the transmission media may be the fluid column in the well, and wherein the down hole device contains a vibrating valve that transmits coded fluid pressure pulses that will be decoded at the surface.
Typically the MWD sensors are placed in a cylindrical probe that is located in the central bore of the drill collar. Theses sensors are not affected by the steel of the surrounding drill collar and are able to make measurements continuously while drilling. However, some of the LWD sensors and some of the newer generation MWD sensors can be strongly affected by the surrounding drill collar and have to be located in the external wall of the drill collar. Examples of LWD/MWD measurements that are affected by the drill collar are resistivity, annulus pressure, gamma density, and to some extent natural gamma ray. Quite often the drilling operation will make use of both MWD and LWD measurement systems. In these situations there can be sensors located in both the probe positioned in the central bore of the drill collar and sensors located in the external wall of the drill collar. As a result, some form of communication is required between these sensor systems to coordinate the measurement functions and transmit data to the surface.
Prior art techniques require that the probe located in the central bore of the drill collar and the sensors located in the collar wall contain a wired connection. However, wired connections are very problematic. Therefore, there is a need for a wireless link between the collar sensors and probe. More specifically, there is a need for an electromagnetic (EM) communication between an LWD/MWD probe located in the internal bore of a drill collar and sensor electronics located in the drill-collar wall. These, and many other needs will be met by the invention herein disclosed.